457 



FUTURE DIRECTIONS IN OCEAN SCIENCES 



119 



In the ocean, the amount of organic material transferred verti- 

 cally from the surface to the bottom and horizontally from estuar- 

 ies to shelf waters to the deep ocean is not a simple linear func- 

 tion of primary production; nor are burial rates of organic matter 

 in ocean sediments. The amount of material transported depends 

 on the physical and chemical characteristics of the environment 

 (e.g., rates and mechanisms of nutrient delivery) and on various 

 largely unappreciated characteristics of the species composition 

 and structure of marine food webs in the euphotic zone, deeper in 

 the water column, and in and around the seafloor. Some bio- 

 geochemical cycling processes are summarized in Figure 3-7. 



Panicle Dynamics 



Research in several areas needs to be initiated to improve our 

 basic understanding of particle dynamics. Some of these areas 

 have been mentioned, for example, the cross-shelf transport mecha- 

 nisms and the use of narrow coastal margins with significant sediment 

 inputs to model transport conditions during past times of lower 

 sea level. 



Among other research possibilities is the need to test the wide 

 range of theoretical models for sediment transport that evolved in 

 the past two decades. For example, models have been developed 

 to describe the coupling between slowly varying currents and sur- 

 face gravity waves and to predict resulting sediment transport. 



(^ Respiration/Regeneration J 



\j\r\j\f\/ Particulate Flux 

 Dissolved Flux 



FIGURE 3-7 Schematic of some processes relevant to biogeochemical 

 cycling on the inner continental margin; (DOM = dissolved organic mate- 

 rial; DIN = dissolved inorganic nitrogen; DON = dissolved organic nitro- 

 gen; POM = particulate organic material). From Mantoura et al. [1991). 



